Emergency shut down

[UndCon]

Yesterday I went out for some fun flying with my Quadcopter and managed to destroy a motor and I bent an arm slightly.
The Quadcopter landed upside down on grass and I was not able to turn off motors from radio. The crash was my own fault trying to flip a few times - but my RC-rate was to low(loop was not fast enough).

I cannot tell why the Quadcopter did not respond to stick input to shut down while lying upside down – I think main loop crashed in MultiWii so input was neglected.


I have seen this earlier - when main loop crashes there is no control over motors - they cannot be turned off. I motor died due to this when ESC kept giving throttle as I rushed forward to kill power.

After power was restored all but the wrecked motor was working just fine.

I am thinking of a kill switch - a separate channel straight from the RX to switch to kill main power.
I have this at home: Turnigy Receiver Controlled Switch

Add something that can handle the loads - a sturdy 12V relay to a car can handle 70 A (840 W).
This is to be between LIPO and Powerdistribution to motors
My idea with a kill switch is to be used in case of emergency only, but can be used as throttle cut when moving/carrying your *copter around.

A small weight penalty to save electronics...

If you are using a separate UBEC you still have power to everything except ESC's

Best regards

UndCon

[captaingeek]

sounds like a lot of trouble. this is one of the reasons i use motor stop.

[copterrichie]

I am not into 3D flying so I set the MINTHROTTLE 1050. I have tried the Motor Stop but it does not work to my expectations.

/* Set the minimum throttle command sent to the ESC (Electronic Speed Controller)
This is the minimum value that allow motors to run at a idle speed */
//#define MINTHROTTLE 1300 // for Turnigy Plush ESCs 10A
#define MINTHROTTLE 1050

[c2po]

I agree with captaingeek and copterrichie, but would suggest another solution that works for me.
Set the minimum throttle to a such value that motors will run with a minimum possible speed (in my case it is 1100).
In that case when you block the props with something like grass, your fingers, or any other obstacles (considering that you already moved your throttle stick to the minimum), motors will not have enough power to rotate the props and they will be stopped and might stutter slightly without any immediate damage to a motor or a prop, considering that you will disconnect the power within a next minute or so.
As a usual disclaimer: YMMV.

[UndCon]

I am using minthrottle at lowest possible turning rate

What good is motor stop if main loop crashed?
My way to solve this is outside the arduino code - so you can always turn off your motors no matter what.
A remote switch, a relay and you are done - no big deal.

Obviously my motors got more speed than minthrottle when Quad was lying upside down - or the motor would not burn?
I always turn throttle to minimum and shut down motors to minimize damages.
//UndCon

[copterrichie]

Well, I could be wrong and Alex maybe able to answer this but if the main look locks, then the there would be no PWM signal. The ESCs are suppose the shutdown if there is no signal.

[Alexinparis]

Not exactly.
The PWM are hardware generated by the atmel.
This piece of hardware is on the atmel, but is different of the main hardware running the code.
If the main loop crashes, the hardware generator part continues to run at the last setting.
=> if the loop crashes when you are full throttle, the motors will continue to have a full throttle order until you disconnect them.

[copterrichie]

Interesting!!!

I recall seeing some watchdog timer code on the Arduino site, I wonder if that would be the solution?

http://arduino.cc/forum/index.php/topic,63651.0.html

[cardboard]

i was thinking of a master relay solution as well. For copters and semi long range fpv. If the vehicle landed at a location that i could not immediately get to or simply didn't know were it was i would be able to throw a switch that triggered a relay that effectively cut the battery off from everything. I've lost batteries from having planes not being found until the next day and I imagine there could be far worse scenarios as well, esc or motor overheating, shorting out wires batteries failing with fire in remote scrub land. It is the worst possible thing to happen and i doubt it would but protecting from it before it happens is the best plan of attack.

[copterrichie]

i was thinking of a master relay solution as well. For copters and semi long range fpv. If the vehicle landed at a location that i could not immediately get to or simply didn't know were it was i would be able to throw a switch that triggered a relay that effectively cut the battery off from everything. I've lost batteries from having planes not being found until the next day and I imagine there could be far worse scenarios as well, esc or motor overheating, shorting out wires batteries failing with fire in remote scrub land. It is the worst possible thing to happen and i doubt it would but protecting from it before it happens is the best plan of attack.

Because of the places I have available to fly at, I am very safety minded. Here is one inexpensive fix for the above scenario. I added Fuses (one per ESC/Motor), a glass slow burn in the picture below and Blade fuses in my new build. The reason for not using just one main fuse is, if only one motor/prop overdraw current, the draw may not be enough to cause the one main fuse to blow. If using a 30A ESC, I suggest using a 25 Amp fuse, if the motor draws 30 amps in normal flight, a higher rated ESC is required anyway. If the current draw exceed the 25A fuse due to prop binding or short for some reason, the fuse will blow disabling the connection to the battery.

[cardboard]

very nice idea with the fusses. I like how it is completely autonomous from everything else. Even if you don't have radio contact for one reason or another it can still preform perfectly. A+++

[UndCon]

Hello!

The idea of using fuses was also on my mind but as a secondary solution. 1 fuse / ESC is enough and should be relatively easy to implement into existing designs.
I have center plates from Flyduino and would like to see a redesign of the boards allowing fuses to be used - or bypassed depending on where you solder your battery connectors.


I managed to strip the motor apart and replace the smelly part (stator) with a fresh one from yet another damaged motor that had a damaged rotor and magnets

2 broken motors rearranged into 1 working = back in air

//UndCon

[captaingeek]

i find it hard to beleive that the mwc is locking up unless youve dont somthing to the code. mine have never done that and I've used 1.5 - current.

[c2po]

fuses? another point of failure? watching you quad tumbles down helplessly because of a gust of a wind that caused an overdraw current spike in accelerated motor which will be harmless for controller but will blow the fuse? have you ever seen the fuses on any helicopters? they do not glide really well, you know...

relay? another point of failure? and to throw a switch that triggered a relay that effectively cut the battery off, that was powering a receiver, that was triggering a relay, which was powered from the same battery? so who's going to power it then?

I think all of that it's a bit of over-thinking...

[cardboard]

[quote]because of a gust of a wind that caused an overdraw current spike in accelerated motor[/quote

That is why slow burn fuses would be used, so a spike wouldn't set it off, only a sustained current draw eg: a motor jammed into the ground at WOT.
The relay option is merely a theory and would need some testing to identify issues as you mentioned.

These are all worst possible scenarios which have to be looked at but not necessarily acted upon, flying within your limits is the safest fail safe every though.

[UndCon]

relay? another point of failure? and to throw a switch that triggered a relay that effectively cut the battery off, that was powering a receiver, that was triggering a relay, which was powered from the same battery? so who's going to power it then?

I think all of that it's a bit of over-thinking...

You dont use a separate UBEC do you?

I have mine connected directly to the LIPO and it gives power to all electronics besides ESC's mains.

The relay will be between LIPO and ESC distribution - effectively cutting power to all motors at the same time - and the UBEC is still powering everything even if you hit the kill switch.

How often do you replace relays on your car - I have never done it...
If this solution saves any part of your *copter it is well worth it.

//UndCon

[copterrichie]

fuses? another point of failure? watching you quad tumbles down helplessly because of a gust of a wind that caused an overdraw current spike in accelerated motor which will be harmless for controller but will blow the fuse? have you ever seen the fuses on any helicopters? they do not glide really well, you know...

relay? another point of failure? and to throw a switch that triggered a relay that effectively cut the battery off, that was powering a receiver, that was triggering a relay, which was powered from the same battery? so who's going to power it then?

I think all of that it's a bit of over-thinking...

That is your Option and LIABILITY.

http://www.youtube.com/watch?v=k7Ita1mFMB4

[c2po]

You dont use a separate UBEC do you?

Nope, I don't, just don't see a need when a whole electronics including receiver, MWC, bluetooth, and whatever else, hardly pull 200mA total at max, I do not have any high current digital servos like on a single rotor heli that can spike up to several amps and where separate switching BEC is a must, and I do have them there. But I still don't have any relays, and the kill switch is called "throttle hold".

I have mine connected directly to the LIPO and it gives power to all electronics besides ESC's mains.
The relay will be between LIPO and ESC distribution - effectively cutting power to all motors at the same time - and the UBEC is still powering everything even if you hit the kill switch.

Fair enough... but relay plus switch plus wiring means additional weight, cost, mounting place, soldering joints, labor, etc... I prefer simple and light.
If I would start thinking of all worst possible scenarios I would probably never was going to fly.

[c2po]

That is your Option and LIABILITY.

http://www.youtube.com/watch?v=k7Ita1mFMB4

That's exactly right, and that's why looking at how some people do a soldering job and knowing what is inside a 10 dollar motor with windings all over the place touching each other and rubbing against sharp casing of a motor I would never say it was an ESC fault.
I also started with cheap motors, but after spending hours and days fixing and insulating loose wiring and replacing bad bearings (like in three motors out of four), and cost of two bearings was more than cost of a motor - I have now a proper place for those motors called trash can.

Now you look at that video and go tell that guy he needs fuses in case of a prop strike or a motor jammed into the ground...

http://vimeo.com/28246917

[copterrichie]

Just a I figured, Thanks.

[c2po]

Guys, sorry, I didn't mean to sound negative. We are all DIY-ers and all love our hobby and all like to tinker with the stuff. We just do some things differently either from our own experience or from experience of others, and we share that experience in the forums, that's what the forums are for. I admire all hard work you people do to develop and improve that nice project, thanks to Alex and all who helped him we all were able to fulfill our dream to fly, it doesn't really matter what equipment/look/weight/color/shape that flying object has.
Sometimes I can be quite sarcastic, please don't take it personal, I respect you all and never intend to offend anyone.

[UndCon]

No apologies needed - no offence taken.

I was just surprised about your approach to the problem.

I will try my Quad once more now that I repaired/replaced the broken motor - but I will have to try with a different prop, 10*4.7 instead of 10*4.5

I know since before that you can have different props without any problems - the software adjusts motor rpm accordingly.

[c2po]

but I'm not really sure what do you mean - my approach to what problem?

[UndCon]

The original problem of course - why I could not turn off motors with the usual stick input.
I felt like your way to solve it was - "buy a new motor if you crash" but I want to save the gear
(mainly 'coz it takes ages fr HK to restock motors)

I intend to go FPV with my quad. If I crash in an area less than 10 seconds away I want to be able to turn off everything to minimize damages.

I can upload the video from the crash but it is really nothing to see or hear to tell what caused the problem.

//UndCon

[c2po]

Well, I really don't know what to suggest because I think the reason why the copter did not respond to stick input is still unknown... right?
I doubt it was a main loop that crashed, microprocessors a usually very robust and keep ticking until the power is lost, but if the power was lost then PWM on the outputs would disappear and ESC should have shut down.
But another reason could be that receiver lost connectivity somehow, either from losing power for a moment from the shock of a crash, causing it to reboot, or maybe because antenna was stuck to the ground blocking the RF signal - but in that case the idea of having remote kill switch won't work since the receiver won't pass the signal to the switch. With 2.4GHz it takes a small obstacle to if not completely block the signal but at least reduce it by four-five times.

It's really hard to tell without seeing the details of the copter layout and how exactly the crash happened, so I guess only you would be able to track that down. But my guess would be that the RF link was lost which caused no response to input.
In that case I cannot really think of any robust solution (nor have I seen one yet) to shut down all the power automatically, I mean such a solution that would not possibly interfere with the normal operation of the copter, because you don't want it to kick in when it is not supposed to.

[c2po]

One idea I can come up with would be to utilize such a feature of some modern accelerometers (for instance BMA180) as capability to detect a shock situation up to 16 g. In that case shock alert interrupt signal can be used to shutdown the motors immediately.
That of course would require some research and experimentation, I guess the shock settings can be set up that way to trigger it only in case of a hard crash, or even a rough landing...

[UndCon]

That is a really good idea. A G-logger

[lalalandrus]

Cheap and easy solution. Take three iron magnets. Solder battery to one. Escs to one. Make a three magnet sandwich. Crash will disconnect them. Change diameter of magnet to survive vibes but not crashes.

Make sure the feed wires are well secured and only the middle magent is free.

[ziss_dm]

Hi UndCon,
I think, you can clamp RESET pin of the arduino to the ground with simple RC switch. It would shutdown PWM and motors should stop in couple of seconds. (You can try to press and hold Reset button on arduino).

regards,
ziss_dm